Our invention deals with hydraulic control systems, and is directed more particularly to one for a hydrostatic transmission for vehicles.
As is well known, vehicles such as some off-highway work vehicles incorporate hydrostatic transmissions wherein a bidirectional, variable-displacement drive pump is connected in fluid circuit with a bidirectional, variable-displacement propelling motor for driving same. A charging pump is also connected to this circuit for supplying positive pressure required. A problem with this type of vehicular transmission is the almost unavoidable oil leakage from the drive pump and the propelling motor during the operation of the vehicle. As the charging pump becomes unable to compensate for such leakage, localized gaseous conditions in the liquid stream, known as cavitation, will develop in the drive pump and the propelling motor. Cavitation presents a serious hazard to these hydraulic units, possibly destroying them unless the vehicle is stopped immediately.